Photoelectrochemical Characterization of Semitransparent WO[sub 3] Films

Abstract

Tungsten trioxide films on transparent substrates ͑glass and F:SnO 2 or indium-tin oxide coated glass͒ were prepared by various methods like doctor-blading, dip-coating, layer-by-layer painting, and spin-coating. Films of up to 10 ϫ 10 cm were grown and characterized by X-ray diffraction, scanning electron microscopy, optical reflectance and transmittance, and photoelectrochemical measurements. Well-crystallized WO 3 with monoclinic structure prevails on all substrates after annealing at or above 550°C. Films grown via layer-by-layer painting and spin-coating using organic precursors consist of WO 3 particulates of around 50 nm. Such films are specular and highly transparent outside the bandgap. Their photoactivity extends up to 470 nm and junctions with 0.1 M HClO 4 yield incident photon to current conversion efficiencies values above 0.9 at 313 nm and 0.1 at 436 nm. Under solar illumination, photocurrents of up to 0.91 mA/cm 2 ͑front-side illumination͒ and 0.67 mA/cm 2 ͑back-side illumination͒ were drawn.

Morphology-Tailored Synthesis of Tungsten Trioxide (Hydrate) Thin Films and Their Photocatalytic Properties

“…WO 3 is an n-type semiconductor with a band gap ∼2.6 eV, which can utilize ∼12% of solar spectrum. 28 Moreover, it shows a high stability in acid bath. These advantages make it a promising candidate in photocatalytic degradation of organic compounds and water splitting to produce hydrogen.…”

Photoelectrochemical Behavior of Nanostructured WO3 Thin‐Film Electrodes: The Oxidation of Formic Acid

“…[32][33][34] A direct mechanism involves inelastic transfer of photogenerated valence-band holes to filled energy levels located in the bandgap and associated with surface-bound species. In contrast, the indirect mechanism takes place via surface-bound OH s C radicals photogenerated at the first step of water photooxidation (H 2 O + h + !OH s C + H + ; h= hole).…”

“…[30][31][32][33] More recently, WO 3 thin-film electrodes have been prepared by different techniques such as doctor-blading, dipcoating, layer-by-layer painting, and spin-coating and their photoactivity tested and compared in 0.1 m HClO 4 solutions. [34] In addition, the photoelectrochemistry of electrodeposited WO 3 nanostructured thin films as regards water and simple organic photooxidation has been investigated in connection with the behavior of TiO 2 /WO 3 nanocomposite electrodes. [35,36] From a broader perspective, a number of articles have appeared on the behavior of nanostructured electrodes used as photoanodes for the oxidation of organic species dissolved in water.…”

Photoelectrochemical Property of Tungsten Oxide Films of Vertically Aligned Flakes for Visible-Light-Induced Water Oxidation

“…1a͒. 10,12 The grain boundaries also seem to act as recombination centers to reduce the lifetime of photoexcited carriers. Conversely, films of platelike crystallites vertically arrayed to the substrate are expected to exhibit photoelectrochemical performance superior to that of films with a large number of grain boundaries ͑Fig.…”